1. Field of the Invention
The present invention relates generally to a fluid-filled elastic mount used as a vibration damper such as an automobile engine mount, which has a fluid chamber filled with a non-compressible fluid, and more particularly to such a fluid-filled elastic mount wherein the pressure of the fluid in the fluid chamber is regulated by utilizing a force generated by an electrostrictive/magnetostrictive element, to enable the engine mount to exhibit different damping characteristics depending upon the type of the vibrations received.
2. Discussion of the Prior Art
As a vibration damper for flexibly connecting two members in a vibration system or mounting one of the two members on the other member in a vibration damping fashion, there is known an elastic mount interposed between the two members of the vibration system. The elastic mount has an elastic body interposed between and elastically connecting a first and a second support which are respectively fixed to one and the other of the two members of the vibration system. This type of elastic mount may be used as an engine mount for a motor vehicle, for example.
Recently, there have been proposed various types of fluid-filled elastic mounts adapted to exhibit sophisticated damping characteristics, wherein the elastic body which elastically connects the first and second supports partially defines a fluid chamber filled with a non-compressible fluid. The fluid chamber is also partially defined by an oscillating plate, which is oscillated or displaced to change the fluid pressure in the fluid chamber depending upon the type of the input vibrations received, so that the specific vibrations can be suitably damped or isolated.
An example of such a fluid-filled elastic mount is disclosed in JP-A-60-8540, wherein the oscillating plate is actuated or oscillated by an electromagnetic force produced upon energization of a solenoid coil, for example. However, such an electromagnetic force is found unsatisfactory to provide a sufficiently large magnitude of a force to actuate the oscillating plate. Another type of fluid-filled elastic mount is disclosed in JP-A-2-42228, wherein the oscillating plate is actuated by using an electrostrictive element made of a piezoelectric ceramic material.
While the electrostrictive element can produce a large magnitude of a force to actuate the oscillating plate, the element undergoes a considerably small amount of displacement upon energization thereof, which results in an accordingly small amount of displacement of the oscillating plate. Therefore, the fluid pressure within the fluid chamber cannot be effectively changed by oscillation of the oscillating plate, whereby the elastic mount cannot provide different damping characteristics depending upon the type of the vibrations received. Thus, the known elastic mount is practically unsatisfactory in its damping characteristics.